دانلود رایگان مقاله خواص رئولوژیکی سوسپانسیونهای نانو کریستال سلولز

ABSTRACT

Rheological behavior, including linear and nonlinear, as well as transient rheology of nanocrystalline cellulose (NCC) suspensions was studied in this work. Two kinds of polymer solutions, aqueous poly(vinyl alcohol) (PVA) with flexible chain structure and aqueous carboxymethyl cellulose (CMC) with semi-rigid chain structure, were used as the suspension media to further explore the role thatthe interactions among NCC and polymers played during shear flow. The results reveal that NCC has lower values of percolation threshold in the PVA solution than in the CMC one during small amplitude oscillatory shear (SAOS) flow because the flexible PVA chain has higher adsorbed level onto NCC particles than the negatively charged semi-rigid CMC chain, which is further confirmed by the Fourier transformed infrared (FT-IR) spectroscopy tests. As a result, the NCC suspension shows a weak strain overshoot in PVA solution during large amplitude oscillatory shear (LAOS) flow, which cannot be seen on the one in CMC solution. During startup shear flow, both ofthese two suspensions show evident stress overshoot behavior with the strainscaling characteristics, indicating the formation of ordered long-term structure of rod-like NCC particles with self-similarity during flow. However, NCC suspension have far stronger stress overshoot response in CMC solution relative to the one in PVA solution. A possible synergy mechanism between NCC and CMC chain is hence proposed.

4. Conclusions

NCC particles can be dispersed well in both the PVA and CMC aqueous solutions, forming stable suspensions. Relative to the semi-rigid CMC with negative charge, the flexible PVA has much stronger interactions with negatively charged NCC particles, leading to a lower percolation threshold of NCC in the PVA aqueous solution during SAOS flow and to a weak strain overshoot behavior during LAOS flow. Both are caused by the formation of flocculation structure of NCC. Besides, the two suspension systems show evident stress overshoot response during startup shear flow, revealing strain-scaling characteristics, which is caused by the formation of long-term ordered structure of NCC particles in the polymer solutions. Butthe overshootlevel is very sensitive to the chain structure of used polymers and their interactions with NCC particles.